Method of making rolled products



Patented July 20,1937

UNITED s ATEs METHOD OF MAKING ROLLED raonuo 'rsp I V v V Duncan P.Forbes, Erwin J. Mohr, and Fritz W.

Meyer, Rockford, Ill., assignors to Gunite Foundries Corporation,Rockford, 111., a cor-1 poration of Illinois No Drawing. ApplicationMarch 11, 1933,

Serial No. 660,440

13 ClaimS.-- (Cl. 148-12) This invention relates to the manufacture ofrolled products of graphitic iron and we have successfully made rolledsheets, plates and bars of such metalby the methods herein set forth.

By the term graphitic' iron we mean iron .containing any form orprecipitated free carbon, and by the term graphite we mean such freecarbon. v

The invention proved and novel method for .the manufacture of ,rolledshapes ofgraphitic iron wherein the cost of manufacture and the timerequired to carry out the method are materially reduced and whereinnumerous difficulties incident to the manufacture of such products areovercome.

I The products are novel and commercially useful materials havingamongother properties advantageous corrosion resistant qualities; Thesement brings about favorable rolling conditions and permits greaterreductions at each pass through the rolls, there are certaindisadvantages to such a method. For example, when the composition of themetal is such that longheating periods are required to decompose thecementite, decarborization of the surface of the ingots may occur..Furthermore, it will be obvious that certain expense is involved insuch heat treatment for fuel in heating the furnace and labor intransferring the ingots. Furthermore, thisheat treatment consumes acertain amount of time which in some instances would also bedisadvantageous. We have found'through the actual manufac ture of suchproducts that certain advantages will accrue from rolling the white ironingots as such without prior heat treatment. We have found that byrolling the white iron directly, the rate of decomposition of thecementite may be accelerated and that the cementite will be largelyeliminated, and with metal of some analysis may be entirely eliminated,during the relatively short time required for rolling. In other words,the cementite decomposes at a much faster rate while the metal is beingrolled than would otherwise be the-case at the same temperature.Consequently,

contemplates a generally im-- when-the metalis rolled as ingots of whiteiron, the cementito willbejentirely or largely elimi nated during therolling operations, thusfeither entirely obviating the'necessity forheating the metalto decompose the cementite' or greatlyv reducing, thetime required to bring lthis labout,

Therefore, inmost instancesa great economy is I effected byproceeding'directly to the heat treating of metal to produce any of aplurality of.

matricesor complete the elimination of combined, carbon from the metaFashereinafter described, while the metal is still in the heat of rolling.

The first step in the method consists in the production of suitable"ingots'ofwhite cast iron. The ingots may have any convenient size orshape and may be formed by pouring'into metal molds; green or dry sandmoldsgorcore sand, or {any other molds customary in foundry practice;The

analysis of this iron willdepend to some extent upon the heat treatmentadopted and upon the ultimate product desired, as "will presently fbedescribed. The ingots will'contain a certainp'roportion of massivecementite (iron carbide) which under heattreatment can'be' decomposedwith a resultant precipitation of graphite in the metal. Unles'sotherwise expressly statedqthe' term cementite used throughout thisspecification and the appended'claimsis intended to mean iron carbide asa distinct crystalline constituent formed upon solidificationof themetal and; not cementite formed at temperatures below this point. Weheatv these white'iron ingots to a rolling temperature and while at thiselevated temperature roll the-ingots into the'desired shapes, such assheets, bars, and the like.

Our experience teaches us'that in general" the rollingcan best becarried out at temperatures between about 1800 F., and the temperatureat v which a liquid phase begins' to appear in the metal. Inmost casesthis will be about'i2l00" F. It may begpossible, however, with metal ofcertainanalysis to roll at slightlyylower temperatures,-but, in general,it seems that the best rolling temperature is the highestternp'erature'ob-' v tainable without the presence 'of a liquid phase.

.Any conventional rolling mechanism'may be employed, but it will befound that as rolling pro ceeds, the operation becomes. increasinglydiffi cult. wehave found to be 'due to the rapid I V v drop intemperature of the iron and the rapid decrease in ductility with changein temperature.

However, ifthe'metal is reheated one or more times during the rolling tomaintain the temper- I ature above'about 1800 F.', the'desir'edreduction in section may be satisfactorily accomplished.

It is; therefore, advisable to locate the heating furnace in suchproximity to the rolling process as to prevent excessive loss intemperature of the metal between the heating furnace and the rolls. Careshould be taken to select the proper amount of reduction at, each pass.The amount of reduction at each pass will depend upon the temperatureofthe metal as it enters the rolls, the type of billet,'the type ofmill, the

contemplates various forms adapted to produce a product of commerciallyusa ble characteristics and involves the heat treatment'of the metal,the type of heat treatment depending upon the ultimate product desiredandthe analysis of the metal. Thus, in order to produce a product ofpredetermined physical characteristioawe control both the analysis ofthe 'metal'and the heat treatment,

imparted to the metal. This heat treatment also results in theproduction of uniform products from rolled materials which mightotherwise have uncertain and erratic'microstructure; The

heat treatment thus serves two purposes, that of bringing the parts, ofeach rolled form and also the various rolled forms touniformity andthat.

of imparting desired, structural characteristics to the material.

, One purpose of thepresent invention is to produce a rolled graphiticiron wherein the graphite is distributed in a matrix of ferrite. Toproduce such a material, we may take 'a'rolled material,

formed in the manner above described, from white iron ingots capable ofbeing graphitized and hav ing a carboncontent preferably not less than1.5%, a percentage of carbon plus a percentage of silicon greater thanabout 2.9%, and a manganese content which is twice the percentage ofsulphur plus about .10% to 30%. When this iron is such that thepercentage of carbon is about 1.5% to 2.20% and the percentage of carbonplus the percentageof silicon content is greater than 3.10% preferablyabout 3.5%, the cementite of the metal will have been completelydecomposed during the rolling operation, while with metal falling withinsubstantially theremainder' of the, first above-mentioned range there isapt to be a' certainamount of residual cementite after the rollingoperations are completed. After the rolling operations, the rolled metalis placed in a furnace and is .held within the graphitizing range (withmost metals between 1350 F. and 1750 F.)

until the cementite has been completely broken down. Where the metal isofan analysis such that the cementite is completely'broken ,down' posedto form graphite. The metal is then.

cooled to atmospheric temperature, preferably at a rapid rate. Theresultant product willbe material having the graphite in elongatedsubstantially parallelly arranged form dispersed in a matrix of ferrite.Examples 1' and 2 are given by way of illustration, Example 1illustrating the manner in which a material may be made wherein thecementite is completely decomposed during the rolling operations, whileExample 2 illustrates the method wherein the metal as it comes fromtherolls'contains some residualcementite.

IExamplc 1.--'-An ingot of %"'thickness was prepared of white iron ofthe following analysis:

, Carbon 1.7%, silicon 1.65%, manganese 30%, sulphur .08% phosphorous.10%.

p This ingot was heated to 1950 F., and as soon as it had reached .asubstantially uniform temperature was rolled into sheets of a thicknessof inch using a reduction of approximately 15% for each pass through therolls. (We have used a 30% reduction at each pass with satisfactoryresults.) When the tem- 1 perature of the'metal dropped below about 1800F., it was reheated to 1950 F. and rolling continued until the desiredsize and thickness of sheet was obtained, reheating as frequently asnecessary to keep the material in reliable condition. After rolling wascompleted, the material was placed in aheat treating furnacebeforeexcessive loss of temperature hadoccurred and was held at about 1350[F.fortwelvej hours. It was then removed from the furnace and allowed tocool'in air.

Example Zr-An ingot was prepared of white iron of the ffollo win ganalysis: Carbon 2.40%, silicon .90%', manganese".30 sulphur .08%, andphosphorous .16 Thesewhite iron ingots were heated to 1950 F. and rolledas soon as they hadreached uniformtemperature using a reduction of aproximately 15 for each pass through the rolls. 'As described in Example1, the metal was reheated as frequently as necessary to maintain it incondition. After rolling was completed, the

material was placed in a heat treating furnace before excssive loss oftemperature had occurred and held'at about 1700 F.'for eight hours. Themetal was then cooled in the furnace to 1350" F.

and held for twenty-four hours. Thereafter the allowed to cool in air.

In both Examples 1 and'2, the final product consisted of a rolledgraphitic iron wherein the graphite or tempercarbon was in the form ofelongated susbtantially parallelly disposed deposits in a matrix offerrite.

However, as previously pointed out, valuable described and immediatelyafter the rolling 'oper-' ations the rolled metal was coiled toatmospheric,

temperature. The resultant product consisted of a matrix which waslargely pearlitic but con tained a small amount of massive cementite andelongated parallel deposits of graphite.

Example 4.-White iron ingots. having the analysis given in Example 2were rolled as therein describedand the rolled metal was allowed to coolto atmospheric temperature immediately after rolling. The productcontained no massive cementite, and the matrix was largely pearlitichaving elongated substantially parallelly disposed deposits of graphite[The lnvention'also contemplates the production of rolled shapes whereinthe matrix consists 7;

of pearlite or sorbite. For the production of such a product, we preferto start with a white iron which has a'carbon' content'preferablynotless than about 1.5%, a percentage of carbon plus a percentage ofsilicon content greater than about 2.9%, and a manganese contentwhich'is twice pletely decomposed during the rolling operations.

These white iron ingots are rolled, as previously described, and thenplaced in a heat treating furnace. that there will be residual cementitein the metal after the completion of the rolling operations, the

metal is held at a temperature within the graphitizing range until thecementite has beencompletely decomposed. The metal 'iisthen brought toabove the critical temperature, but preferably not more than about 200F. thereabove and is then cooled through the critical temperature at aspeed such as to'retain the combined carbon in the matrix in the form ofpearlite or sorbite. The best results are usually obtained when coolingtakes place rapidly in air. Examples 5 and6 are given by way ofillustration, Example 5 illustrating a method wherein the cementiteiscom pletely decomposed in the rolls, and Example 6 showing a methodwherein the product of the rolling operations contains residualcementite.

Example 5.A white iron ingot having a carbon content of 1.70%, silicon1.65% ,manganese sulphur .08%, and phosphorous '.10% was heated to about1950 F. and rolled as soon 'asthe metal had become uniform intemperature, using a reduction of about 15% at each pass, the metal.tially uniform in temperature.

the rolling operation was then placed ln'a heat being reheated asfrequently as necessary to maintain it in rolling condition. The metalwas then placed in a heat treating furnace and brought to about 1600 F.only long enough to" secure uniform temperature. Thereafter the metalwas cooled rapidly to atmospheric temperature as by cooling in air. i l

Example 6.A white iron ingot was made of the following analysis: Carbon2.40%, silicon .90%, manganese .80%, sulphur .0'1%, and phosphorous.16%. The ingots were then heated to about 1950 F. and rolled asdescribed "in the first example as soon as it had become substan- Theproduct of treating furnace and brought to about 1700" F. for eighthours, and was then broughttoa'uniform temperature of about1600 F. andthereafter cooled rapidly through the critical temperature to roomtemperature, forexample, as by cooling in air.

The products of the methods described in Examples 5 and 6 showed apearlitic matrix containing elongated clusters of graphite or tempercarbon.

The invention also contemplates-the produc-' tion of products whereinthe matrix consists-of spheroidized eutectoid cementite distributedthrough ferrite crystals. In making such a prod uct, we prefer to roll awhite iron ingot wherein the carbonis preferably notless than about1.5%,

the percentage of carbon plus the percentage of silicon is greater thanabout 2.9%; and the man- 7 Where the analysis of the iron is suchpercentageof sulphur plus 30% .to ..80%.' "The ingots are heateddirectly to the rolling tem perature and rolled, as previously,described. The' product of the.rollingfoperation-s' is placedfin a 3'ganese content, isabout twice-the percentage of sulphur,plus';.10% to.80%, preferablytwice the.

furnace andheld ,within-fthe. graphitizing range until the'residu'a'lcementite has been-complete ly decomposed f-The metahis then cooledthrough the critical temperature at a {speed such as to retain thecombined carbon in thematrix in the form'of pearlite or sorbite, asfor'example by cooling in air, and is thenheld at or reheated to thespheroidizing range "(about.,1200 to 1300, 'F.) ,foras'ufficienttimetofspheroidizethe p'earlite oi sorbite to thedesired degree. .Ex

ample "'Ij'is given by. way of'illustra'tion I of a satis-.,

factorymanner of producing this type of product.

exam le 7.-'-A whitefiron. ingot having" the analysis set forth 'inflEx'ample 5was madeand rolled in the mannerjalready described, After thematerial had been rolled to'the desired shape it was held at about17.00" F. for about eight hours and was then cooled at the rate ofaboutf600'" per hour through the "critical temperature (in this caseabout-1375f F. ),.Jand thenheld at'a temperature ofv about1 275 F. fortwenty-four hours. It' was thereafter cooledto roomtemperature. Thismetal had a matrix of finely spheroidized' cementite uniformlydistributed through ferrite crystals and elongated. substantiallyparallelly disposed. deposits of. graphite were embedded in this matrix.I a f It iwillbe seen that in our process we use as a starting "pointwhite iron and proceedto roll this metal at'an elevated temperature. Inthis way, we are enabled to materially accelerate the. v

rate at which the cenientite is decomposed, thereby materiallyfreducing'the time required for the production of certain desirable product's. By

properly regulating the analysis of the metal, we are enabled to bringaboutcomplete decompositionof the cementite during the rollingoperations, thereby completely 'eliminating the necessity for 'holdingthemetal at anelevated temperature. until the 'cementite has beendecomposed. In those instances wherev the cementite is not completelydecomposed during the rolling of the metal, the .heattreatnient requiredfor the completion of this decomposition is greatly reduced in. time andmay be combined withsome other subsequent heat treatment'and be carriedout in the same furnace, as .a-preliminary' step of such heat treatment.Inthis manner, frequent transfers or" the "metal from 'fumace ,to'

furnace is eliminated and aconsiderable saving inheat and timeisefiected since whatwould; otherwise be two separate heattreatments arecombined intoa single continuous treatment at" required temperatures.

cementite' will depend to a certain degree upon .the extent of theworking of the metal but in commercial operations the reduction ofsection is usually suflicient toresult in the decomposition of at leasta large part of thecementite and ;60 The amount of the decomposition ofthe when the analysis is favorable, as, herein, de-.

. scribed, allof the cementite' will be decomposed;

Some allowances will have to be madefwhen the rolling operations departfrom the customary reductions.

As one phase ofou'r invention, we regulate the analysis of the whiteiron, and, after rolling,

subject the'rolled'materialto certain heat treat ments to produceuniformproduots of definite,

yet variable physical properties. This heat treat ment normallyservestwo purposes. It serves first to produce resultant products ofcertain-predetermined physical properties,thereby enabling us to produceproductssuitable and valuable for certain definite requirements;However, in'addivtion to this function of the heat treatment, the

steps also serve to bring'the'rolled metal into uni formity regardlessof the particular nature of its matrix; It will be understood thatduring and prior to'the rolling operations the'ingots are sub:

jected'to variable conditions so that in many instances there will bea'variation in the microstructure of the metal of the different ingots,and frequently a variation in the microstructure of various parts of thesame sheet or bar rolled from an ingot. Forsome uses the'metal will, ofcourse, be satisfactory regardless of these variables.

However, the heat treatment after the rolling operations serves toovercome this lack of funiformity so that the productjffof themethod mayhave uniformity throughout each piece and throughout the various piece 1New and novel products result from the method above disclosed, suchproducts being described and claimed in our above-mentioned copendingapplication. These products have certain new and commercially valuableproperties. Cast iron and metals containing graphite have long been wellknown for their corrosion resistance properties, particularly .corrosiondue to atmospheric exposure and underground services. For this use themetals must in many cases be thin in section; In the past, metals forthis purpose have been non-ferrous metals or steel alloys which containsubstantial quantities of other metals, such as chromium, copper,nickel, etc. These alloys are relatively expensive. The difficulty hasbeen that while iron containing graphite has in the past been available.in the form ofindividually'cast platesfthere is a limitationto theminimum section which can be cast of graphite bearing iron.

That is, in the past there has been no method of making graphitebearingiron' in sheets of sufficient size and thinness of section topermit the generaluse of such metals for corrosion resistance purposesor for other 'purposesto which such' metal in the sheet form might beadapted. ,Our method completely obviates this difficulty and permits therolling of such metal in very thin section and in relatively largesheets. The method brings about the production of uniform sheets ofgraphite bearing metal of predetermined properties with almost the'samefacility with which steel sheets are made, thus opening up a largevariety of new materials for the. sheet metal industry. 'I'he'methodalso permits the production of graphite bearing metal in shapes andsizes which have heretofore not been obtainable.

A number of uses for the metals made in accordance with our method mightbe listed. The

metal made in accordance with Examplesl and 2 is valuable for use infabrication where draw ing and forming operations are necessary.- Themetal made in accordance with Examples 5 and 6 will be of particularvalue-where wear' resistance and corrosion resistance are important,such, for

example, as in the manufacture of elevator buckets. Metal made inaccordance with the seventh example possesses corrosion resistance aswell as high strength and ductility, and is of a particular valuein themanufacture of such materials as ship plates, coal hoppers, .tanks,andthe like. Q '1 We'have dealt} throughout this specification with thecompositionof the metal as this is concerned withcertain'well known'constituents. It

will vbe understood, however," that numerous other elementsmay bepresent in the metal or may be added thereto which will or mayv effectthe method or the product-some beneficially and some otherwise.

' While we havethus described and illustrated specific embodiments ofour invention, we are aware that numerous. alterations and changes maybe made without departing from the spirit of the invention and .thescope of theappended claims; in which- We claimi V l L'Themethod fortreating graphitizable white cast iron containing a graphitizingagent toac,- ceierate'the decomposition of the cementite which includes heatingsaid iron the. temperature above about 1800 F. and thereafterplastically deforming the same.

2. The method of rolling sheets, bars, and'other shapes'fromgraphitizable white cast iron containingagraphitizing agent wherein thedecom position of the cementite of the iron is accelerated byhot.rolling of the metal above about 1800 F. and the metal is,thereafter held at -atemperature within the graphitizing range todecompose the residualfcementite.

a. The method of making rolled shapes er graphitio iron, comprisingbringing to the hot rolling temperature white iron wherein the-carbonis'about 1.5% to about 2.0% and the percentage of carbon plus thepercentage of silicon manganese equal to twice the percentageof sulphurplus .10% to .80%, rolling said iron, heat I treating the same in thegraphitizing range to decompose the cementite remaining after theroll-..

ing operations and cooling at a rate to produce a pearlitic matrix.- I'5. The method of making rolled shapes of graphitic iron, comprisingbringing to the hot rolling temperature above about 1800 F.'white ironwherein the carbon content is between about 1.5 and 2.20% and thepercentage of carbon plusthe percentage of silicon is not. less,thanabout 3.10%, rolling saidiron and cooling said iron from-a pointslightly'above the critical temperature at a speed such as to retain thecombined carbon in the matrix in the form of pearlite.

6. The method of making rolled shapes of graphitic iron comprisingbringing to the hot rolling temperature above about 1800 F. white ironof an analysis within the following limitscarbon not less-than about1.5%,percentage of carbon plus percentage of silicon'greater than about2 .9%, manganese, equal to twice the per-x centage of sulphur plus 110%to .80%, rolling said iron to deform the same and decompose the majorportion of the cementite thereof, thereafter hold-' ing, the same at atemperature within the graphitizingrange to decompose. the residualcementite,

cooling the iron from a point'slightly above thecritical temperaturethrough the critical temperature at a speed such as to retain thecombined carbon in the matrix in the form of pearlite, and then holdingthe metal at a spheroidizing temperature to spheroidize the pearlite.

7. The method of making rolled shapes of graphitic iron which consistsin producing ingots of white cast iron containing a graphitizi'ngagent,causing said ingots to be brought as ingots of white cast iron to atemperature above about 1800 F. but below the temperature at which aliquid phase appears in the metal of said ingots, and reducing saidingots to rolled forms of a desired by rolling the ingots first while atsubstantially saidhigh temperature and then successively while theingots are at atemperature above about 1800" F., reheating of the ingotsbetween successive rolling operations being resorted to when necessaryto maintain the ingots at a temperature above about 1800 F. until soreduced.

8. The methodior making rolled shapes of graphitic iron wherein whiteiron containing a graphitizing agent is rolled at temperatures aboveabout 1800 F.

9. The method for making rolled shapes of V graphitic iron wherein ironcontaining a graphitizing agent is rolled as ingots of white iron at atemperature above about 1800 F., and therolled metal is then held at atemperature in the graphitizing range until the massive cementite issubstantially completely decomposed.

10. The method of making rolled shapes of graphitic iron comprisingbringing to a hot rolling temperature above about 1800 F. an iron carbonalloy of an analysis within the following limits-carbon not less thanabout 1.5%;, percentage .of carbon plus percentage ofsilicon greaterthan about 2.9%, manganeseequal 'to twice the percentage of sulphur plusabout .10%

to 30%, hot rolling said metal at a temperature above aboutl800" F. andthereafter subjecting the rolled metal to a heat treatmentln thegraphitizing range to precipitate at least .a

portion of the combined carbonjas graphite;

11. The method of'making rolled shapes of graphitic iron, comprisingbringing .to the hot rolling temperature above about 1800 F. an'ironlcarbon alloy wherein the carbon is about 1.5% to about 2.2% andthepercentage of 'carbon plus. the percentage of silicon is not lessthan about 3.10%, andhot rolling said metal to deform the 3 sameanddecompose the cementite.

12. The method for making rolled shapes of graphitic iron wherein ironcontaining a graphitizing agent is rolled as ingots of white iron atcompletely decomposed and is then subjected to a heat treatment todevelop a predetermine microstructure ofthe matrix. I a

13. The method'for making rolled shapes of graphitic iron wherein ironcontaining a graphitizing agent is rolled as ingots of white iron at i 0temperatures above about 1800 F; to deform the same and decomposexthecementite, and is thereafter subjected to a heat treatment to develop aa 2'0. temperatures above about 1800" F., the rolled metal is then heldat a temperature in the graphi- 1 -tizing range until the cementite issubstantially

